In this video I show what my current approach on how to master a song. Even though I would never consider myself to be a mastering engineer, it isn't usual for me to send out a mastered version of my mix to the client.
The purpose of doing this is to demonstrate to the client what their mix would sound like once it has been through mastering.
I'm definitely not trying to go for perfection here but rather get it as close as I possibly can. It's really hard to compete with a mastering engineer who has dedicated their entire life to the craft.
I also realize that this is probably a more expensive way to approach mastering your own song but also realize that there are many free options you can use that can mimic what I am doing. I just personally prefer the sound of my mixes going through the analog gear but that shouldn't stop you from making a great record!